Naturally occurring praseodymium (59Pr) is composed of one stable isotope, 141Pr. Thirty-eight radioisotopes have been characterized with the most stable being 143Pr, with a half-life of 13.57 days and 142Pr, with a half-life of 19.12 hours. All of the remaining radioactive isotopes have half-lives that are less than 5.985 hours and the majority of these have half-lives that are less than 33 seconds. This element also has 15 meta states with the most stable being 138mPr (t1/2 2.12 hours), 142mPr (t1/2 14.6 minutes) and 134mPr (t1/2 11 minutes).
The isotopes of praseodymium range in atomic weight from 120.955 u (121Pr) to 158.955 u (159Pr). The primary decay mode before the stable isotope, 141Pr, is electron capture and the mode after is beta decay. The primary decay products before 141Pr are element 58 (cerium) isotopes and the primary products after are element 60 (neodymium) isotopes.
|-| rowspan=3|121Pr| rowspan=3 style="text-align:right" | 59| rowspan=3 style="text-align:right" | 62| rowspan=3|120.95536(75)#| rowspan=3|600(300) ms| p| 120Ce| rowspan=3|(3/2−)| rowspan=3||-| β+ (rare)| 121Ce|-| β+, p (rare)| 120La|-| 122Pr| style="text-align:right" | 59| style="text-align:right" | 63| 121.95181(54)#| 500# ms| β+| 122Ce|||-| 123Pr| style="text-align:right" | 59| style="text-align:right" | 64| 122.94596(64)#| 800# ms| β+| 123Ce| 3/2+#||-| rowspan=2|124Pr| rowspan=2 style="text-align:right" | 59| rowspan=2 style="text-align:right" | 65| rowspan=2|123.94296(64)#| rowspan=2|1.2(2) s| β+| 124Ce| rowspan=2|| rowspan=2||-| β+, p (rare)| 123La|-| rowspan=2|125Pr| rowspan=2 style="text-align:right" | 59| rowspan=2 style="text-align:right" | 66| rowspan=2|124.93783(43)#| rowspan=2|3.3(7) s| β+| 125Ce| rowspan=2|3/2+#| rowspan=2||-| β+, p (rare)| 124La|-| rowspan=2|126Pr| rowspan=2 style="text-align:right" | 59| rowspan=2 style="text-align:right" | 67| rowspan=2|125.93531(21)#| rowspan=2|3.12(18) s| β+| 126Ce| rowspan=2|(4, 5, 6)| rowspan=2||-| β+, p (rare)| 125La|-| 127Pr| style="text-align:right" | 59| style="text-align:right" | 68| 126.93083(21)#| 4.2(3) s| β+| 127Ce| 3/2+#||-| style="text-indent:1em" | 127mPr| colspan="3" style="text-indent:2em" | 600(200)# keV| 50# ms||| 11/2−||-| rowspan=2|128Pr| rowspan=2 style="text-align:right" | 59| rowspan=2 style="text-align:right" | 69| rowspan=2|127.92879(3)| rowspan=2|2.84(9) s| β+| 128Ce| rowspan=2|(3+)| rowspan=2||-| β+, p (rare)| 127La|-| 129Pr| style="text-align:right" | 59| style="text-align:right" | 70| 128.92510(3)| 32(3) s| β+| 129Ce| (11/2−)||-| style="text-indent:1em" | 129mPr| colspan="3" style="text-indent:2em" | 382.7(5) keV| 1# ms| β+| 129Ce| (11/2−)||-| 130Pr| style="text-align:right" | 59| style="text-align:right" | 71| 129.92359(7)| 40.0(4) s| β+| 130Ce| (6, 7)(+#)||-| style="text-indent:1em" | 130mPr| colspan="3" style="text-indent:2em" | 100(100)# keV| 10# s||| 2+#||-| 131Pr| style="text-align:right" | 59| style="text-align:right" | 72| 130.92026(6)| 1.50(3) min| β+| 131Ce| (3/2+)||-| rowspan=2 style="text-indent:1em" | 131mPr| rowspan=2 colspan="3" style="text-indent:2em" | 152.4(2) keV| rowspan=2|5.7(2) s| IT (96.4%)| 131Pr| rowspan=2|(11/2−)| rowspan=2||-| β+ (3.59%)| 131Ce|-| 132Pr| style="text-align:right" | 59| style="text-align:right" | 73| 131.91926(6)| 1.49(11) min| β+| 132Ce| (2+)||-| style="text-indent:1em" | 132mPr| colspan="3" style="text-indent:2em" | 0(100)# keV| 20# s| β+| 132Ce| (5+)||-| 133Pr| style="text-align:right" | 59| style="text-align:right" | 74| 132.916331(13)| 6.5(3) min| β+| 133Ce| (3/2+)||-| style="text-indent:1em" | 133mPr| colspan="3" style="text-indent:2em" | 192.05(14) keV| 1.1(2) μs||| (11/2−)||-| 134Pr| style="text-align:right" | 59| style="text-align:right" | 75| 133.91571(4)| 17(2) min| β+| 134Ce| (5−)||-| style="text-indent:1em" | 134mPr| colspan="3" style="text-indent:2em" | 0(100)# keV| ~11 min| β+| 134Ce| 2−||-| 135Pr| style="text-align:right" | 59| style="text-align:right" | 76| 134.913112(13)| 24(2) min| β+| 135Ce| 3/2(+)||-| style="text-indent:1em" | 135mPr| colspan="3" style="text-indent:2em" | 358.06(6) keV| 105(10) μs||| (11/2−)||-| 136Pr| style="text-align:right" | 59| style="text-align:right" | 77| 135.912692(13)| 13.1(1) min| β+| 136Ce| 2+||-| 137Pr| style="text-align:right" | 59| style="text-align:right" | 78| 136.910705(13)| 1.28(3) h| β+| 137Ce| 5/2+||-| style="text-indent:1em" | 137mPr| colspan="3" style="text-indent:2em" | 561.22(23) keV| 2.66(7) μs||| 11/2−||-| 138Pr| style="text-align:right" | 59| style="text-align:right" | 79| 137.910755(15)| 1.45(5) min| β+| 138Ce| 1+||-| style="text-indent:1em" | 138mPr| colspan="3" style="text-indent:2em" | 348(23) keV| 2.12(4) h| β+| 138Ce| 7−||-| 139Pr| style="text-align:right" | 59| style="text-align:right" | 80| 138.908938(8)| 4.41(4) h| β+| 139Ce| 5/2+||-| rowspan=2|140Pr| rowspan=2 style="text-align:right" | 59| rowspan=2 style="text-align:right" | 81| rowspan=2|139.909076(7)| rowspan=2|3.39(1) min| EC (51.3(22)%)| rowspan=2|140Ce| rowspan=2|1+| rowspan=2||-| β+ (48.7(22)%)|-| style="text-indent:1em" | 140m1Pr| colspan="3" style="text-indent:2em" | 127.5(3) keV| 0.35(2) μs||| 5+||-| style="text-indent:1em" | 140m2Pr| colspan="3" style="text-indent:2em" | 763.3(7) keV| 3.05(20) μs||| (8)−||-| 141Pr[1] | style="text-align:right" | 59| style="text-align:right" | 82| 140.9076528(26)| colspan=3 align=center|Stable| 5/2+| 1.0000|-| rowspan=2|142Pr| rowspan=2 style="text-align:right" | 59| rowspan=2 style="text-align:right" | 83| rowspan=2|141.9100448(26)| rowspan=2|19.12(4) h| β− (99.98%)| 142Nd| rowspan=2|2−| rowspan=2||-| EC (.0164%)| 142Ce|-| style="text-indent:1em" | 142mPr| colspan="3" style="text-indent:2em" | 3.694(3) keV| 14.6(5) min| IT| 142Pr| 5−||-| 143Pr| style="text-align:right" | 59| style="text-align:right" | 84| 142.9108169(28)| 13.57(2) d| β−| 143Nd| 7/2+||-| 144Pr| style="text-align:right" | 59| style="text-align:right" | 85| 143.913305(4)| 17.28(5) min| β−| 144Nd| 0−||-| rowspan=2 style="text-indent:1em" | 144mPr| rowspan=2 colspan="3" style="text-indent:2em" | 59.03(3) keV| rowspan=2|7.2(3) min| IT (99.93%)| 144Pr| rowspan=2|3−| rowspan=2||-| β− (.07%)| 144Nd|-| 145Pr| style="text-align:right" | 59| style="text-align:right" | 86| 144.914512(8)| 5.984(10) h| β−| 145Nd| 7/2+||-| 146Pr| style="text-align:right" | 59| style="text-align:right" | 87| 145.91764(7)| 24.15(18) min| β−| 146Nd| (2)−||-| 147Pr| style="text-align:right" | 59| style="text-align:right" | 88| 146.918996(25)| 13.4(4) min| β−| 147Nd| (3/2+)||-| 148Pr| style="text-align:right" | 59| style="text-align:right" | 89| 147.922135(28)| 2.29(2) min| β−| 148Nd| 1−||-| style="text-indent:1em" | 148mPr| colspan="3" style="text-indent:2em" | 50(30)# keV| 2.01(7) min| β−| 148Nd| (4)||-| 149Pr| style="text-align:right" | 59| style="text-align:right" | 90| 148.92372(9)| 2.26(7) min| β−| 149Nd| (5/2+)||-| 150Pr| style="text-align:right" | 59| style="text-align:right" | 91| 149.926673(28)| 6.19(16) s| β−| 150Nd| (1)−||-| 151Pr| style="text-align:right" | 59| style="text-align:right" | 92| 150.928319(25)| 18.90(7) s| β−| 151Nd| (3/2)(−#)||-| 152Pr| style="text-align:right" | 59| style="text-align:right" | 93| 151.93150(13)| 3.63(12) s| β−| 152Nd| 4+||-| 153Pr| style="text-align:right" | 59| style="text-align:right" | 94| 152.93384(11)| 4.28(11) s| β−| 153Nd| 5/2−#||-| 154Pr| style="text-align:right" | 59| style="text-align:right" | 95| 153.93752(16)| 2.3(1) s| β−| 154Nd| (3+, 2+)||-| 155Pr| style="text-align:right" | 59| style="text-align:right" | 96| 154.94012(32)#| 1# s [>300 ns]| β−| 155Nd| 5/2−#||-| 156Pr| style="text-align:right" | 59| style="text-align:right" | 97| 155.94427(43)#| 500# ms [>300 ns]| β−| 156Nd|||-| 157Pr| style="text-align:right" | 59| style="text-align:right" | 98| 156.94743(43)#| 300# ms| β−| 157Nd| 5/2−#||-| 158Pr| style="text-align:right" | 59| style="text-align:right" | 99| 157.95198(64)#| 200# ms| β−| 158Nd|||-| 159Pr| style="text-align:right" | 59| style="text-align:right" | 100| 158.95550(75)#| 100# ms| β−| 159Nd| 5/2−#|